1. Field of the Invention
The invention relates to a cruise control system and cruise control method that perform cruise control on a vehicle.
2. Description of the Related Art
For example, Japanese Patent Application Publication No. 2001-26226 (JP-A-2001-26226) describes a known vehicle cruise control system that performs cruise control on a vehicle. The cruise control system of a vehicle that follows the vehicle ahead appropriately selects and performs cruise control based on an acceleration or cruise control based on a following distance on the basis of a vehicle speed. The cruise control system attempts to further quickly track the vehicle ahead through cruise control based on an acceleration when the vehicle ahead accelerates in a low-speed state, such as when a road is busy.
However, in the above described vehicle cruise control technique, there is a problem that spontaneous traffic congestion is prone to occur when the amount of traffic on a road increases. For example, while acceleration control or following distance control is being carried out as cruise control, as the amount of traffic of vehicles on a road increases, the speed of the vehicles decreases, so a distance between adjacent vehicles reduces accordingly. Then, as a vehicle brakes with a reduced following distance, the braking operation of the vehicle causes a following vehicle to further strongly brake. Thus, a deceleration due to the braking operation propagates backward while being amplified, thus causing a massive spontaneous traffic congestion.